233 research outputs found
Improved WKB approximation for quantum tunneling: Application to heavy ion fusion
In this paper we revisit the one-dimensional tunneling problem. We consider
Kemble's approximation for the transmission coefficient. We show how this
approximation can be extended to above-barrier energies by performing the
analytical continuation of the radial coordinate to the complex plane. We
investigate the validity of this approximation by comparing their predictions
for the cross section and for the barrier distribution with the corresponding
quantum mechanical results. We find that the extended Kemble's approximation
reproduces the results of quantum mechanics with great accuracy.Comment: 8 pages, 6 figures, in press, in European. Phys. Journal A (2017
Approximate transmission coefficients in heavy ion fusion
In this paper we revisit the one-dimensional tunnelling problem. We consider
different approximations for the transmission through the Coulomb barrier in
heavy ion collisions at near-barrier energies. First, we discuss approximations
of the barrier shape by functional forms where the transmission coefficient is
known analytically. Then, we consider Kemble's approximation for the
transmission coefficient. We show how this approximation can be extended to
above-barrier energies by performing the analytical continuation of the radial
coordinate to the complex plane. We investigate the validity of the different
approximations considered in this paper by comparing their predictions for
transmission coefficients and cross sections of three heavy ion systems with
the corresponding quantum mechanical results.Comment: 12 pages, 6 figure
Post-1995 French cinema: return of the social, return of the political?
A key trend in post-1995 French cinema has been the return of the social. Analysing this trend, this article seeks to evaluate its politic impact. Using HervĂ© Le Rouxâs Reprise (1997) and AgnĂšs Vardaâs Les Glaneurs et la glaneuse (2000) as key meta-texts, it suggests that the current wave of politically engaged cinema needs to be approached in new ways that recognise how films trace the impact of a politically unmediated, ârawâ real on groups or individuals. It further suggests that the withdrawal of political mediation gives the films an essential ambiguity and a melodramatic quality that, rather than mere clichĂ©, may be a privileged way to engage with the violence of the real. Film is now not so much in the van but dans le bain of a diverse socio-political stirring
Identification, cloning and environmental factors modulation of a ab defensin from the Lessepsian invasive mussel Brachidontes pharaonis (Bivalvia: Mytilidae).
Immunological effectors of invasive species playing a role in addressing new colonization are still poorly studied. In the present study the cDNA sequence of the defensin from a Lessepsian invasive species, the Red Sea mussel Brachidontes pharaonis, was cloned using RACE method. Defensins are a class of widely known antimicrobial peptides (AMPs), oligopeptides with a broad spectrum of targeted organisms ranging from viruses to parasites. Analysis of BpDef sequence (262 bp) revealed the presence of an ORF coding for 81 amino acids. The full-length amino acid sequence showed the highest similarity to antimicrobial peptides MGD1 and MGD2 sequence from Mytilus galloprovincialis. Phylogenetic analysis suggested that BpDef belongs to the αÎČ defensin AMPs with a typical domain structurally characterized by a α helix and two ÎČ sheets. BpDef mRNA is located in circulating hemocytes with small intra-cytoplasmic granules and with large granules. The transcription of defensin gene was modulated by the stress from temperatures and oxygenation condition. Temperatures of 20 °C did not stimulate a BpDef transcription over a short time. At 30 °C the kinetics of BpDef gene transcription showed up regulation after one day, while it was down regulated after six days, both under normoxia and hypoxia conditions
The lure of sirens: joint distance and velocity measurements with third generation detectors
The next generation of detectors will detect gravitational waves from binary neutron stars at cosmological distances, for which around a thousand electromagnetic follow-ups may be observed per year. So far, most work devoted to the expected cosmological impact of these standard sirens employed them only as distance indicators. Only recently their use as tracers of clustering, similar to what already proposed for supernovae, has been studied. Focusing on the expected specifications of the Einstein Telescope (ET), we forecast here the performance on cosmological parameters of future standard sirens as both distance and density indicators, with emphasis on the linear perturbation growth index and on spatial curvature. We improve upon previous studies in a number of ways: a more detailed analysis of available telescope time, the inclusion of more cosmological and nuisance parameters, the Alcock-Paczynski correction, the use of sirens also as both velocity and density tracers, and a more accurate estimation of the distance posterior. We find that the analysis of the clustering of sirens improves the constraints on by 30% and on by over an order of magnitude, with respect to their use merely as distance indicators. With 5 years of joint ET and Rubin Observatory follow-ups we could reach precision of 0.1 km/s/Mpc in and 0.02 in using only data in the range . We also find that the use of sirens as tracers of density, and not only velocity, yields good improvements on the growth of structure constraints
Gene expression specificity of the mussel antifungal mytimycin (MytM)
We previously reported the nucleotide sequences and diversity of mytimycin (MytM) from the Mediterranean
mussel, Mytilus galloprovincialis. Using real-time PCR (q-PCR), we observed that the MytM gene
was mainly expressed in circulating hemocytes and to a less extent in the mantle. In vivo challenge with
bacteria or with the yeast, Candida albicans, did not increase the expression as measured by q-PCR in
hemocytes. By contrast, injection of the filamentous fungus, Fusarium oxysporum, induced a sudden and
strong increase of expression at 9h p.i. (stimulation index of 25.7 +- 2.1). Optimum stimulating dose was
104 spores of F. oxysporum per mussel. In the same samples, AMP mytilin and myticin showed no
stimulation. Consequently, we hypothesized the existence of 2 different signal transduction pathways,
one activated by bacteria and yeast, the other triggered by filamentous fungi. A second challenge performed
with F. oxysporum 24 h after the first challenge induced an increase of MytM gene expression
(stimulation index of 3.5 +- 1.7). However, this second increase was significantly lower than the first,
suggesting less efficient response rather than significant protection
Evolution of alternative reproductive systems in Bacillus stick insects.
Reproduction is a key feature of all organisms, yet the way in which it is achieved varies greatly across the tree of life. One striking example of this variation is the stick insect genus Bacillus, in which five different reproductive modes have been described: sex, facultative and obligate parthenogenesis, and two highly unusual reproductive modes: hybridogenesis and androgenesis. Under hybridogenesis, the entire genome from the paternal species is eliminated and replaced each generation by mating with the corresponding species. Under androgenesis, an egg is fertilized, but the developing diploid offspring bear two paternal genomes and no maternal genome, as a consequence of unknown mechanisms. Here, we reevaluate the previous descriptions of Bacillus lineages and the proposed F1 hybrid ancestries of the hybridogenetic and obligately parthenogenetic lineages (based on allozymes and karyotypes) from Sicily, where all these reproductive modes are found. We generate a chromosome-level genome assembly for a facultative parthenogenetic species (B. rossius) and combine extensive field sampling with RADseq and mtDNA data. We identify and genetically corroborate all previously described species and confirm the ancestry of hybrid lineages. All hybrid lineages have fully retained their F1 hybrid constitution throughout the genome, indicating that the elimination of the paternal genome in hybridogens is always complete and that obligate parthenogenesis in Bacillus hybrid species is not associated with an erosion of heterozygosity as known in other hybrid asexuals. Our results provide a stepping stone toward understanding the transitions between reproductive modes and the proximate mechanisms of genome elimination
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